X-Ray Fused With Magnetic Resonance Imaging (XFM) to Target Endomyocardial Injections

Abstract

Background-Magnetic resonance imaging (MRI) permits 3-dimensional (3D) cardiac imaging with high soft tissue contrast. X-ray fluoroscopy provides high-resolution, 2-dimensional (2D) projection imaging. We have developed real-time x-ray fused with MRI (XFM) to guide invasive procedures that combines the best features of both imaging modalities. We tested the accuracy of XFM using external fiducial markers to guide endomyocardial cell injections in infarcted swine hearts. Methods and Results-Endomyocardial injections of iron-labeled mesenchymal stromal cells admixed with tissue dyewere performed in previously infarcted hearts of 12 Yucatan miniswine (weight, 33 to 67 kg). Features from cardiac MRI were displayed combined with x-ray in real time to guide injections. During 130 injections, operators were provided with 3D surfaces of endocardium, epicardium, myocardial wall thickness (range, 2.6 to 17.7 mm), and infarct registered with live x-ray images to facilitate device navigation and choice of injection location. XFM-guided injections were compared with postinjection MRI and with necropsy specimens obtained 24 hours later. Visual inspection of the pattern of dye staining on 2,3,5-triphenyltetrazolium chloride-stained heart slices agreed (ϭ0.69) with XFM-derived injection locations mapped onto delayed hyperenhancement MRI and the susceptibility artifacts seen on the postinjection T2*-weighted gradient echo MRI. The distance between the predicted and actual injection locations in vivo was 3.2Ϯ2.6 mm (nϭ64), and 75% of injections were within 4.1 mm of the predicted location. Conclusions-Three-dimensional to two-dimensional registration of x-ray and MR images with the use of external fiducial markers accurately targets endomyocardial injection in a swine model of myocardial infarction.

Targeted transendocardial therapeutic delivery guided by mri—x‐ray image fusion

“…The lack of a specific target in prior studies limits comparisons of targeting accuracy. The MRI to XRF fusion system described by de Silva et al [17] reported a target registration error of 3.2 AE 2.6 mm but this was calculated based only on the predicted versus actual location of the injection, with no reference to the target region (infarct). We calculated error using the target region as the reference because it directly characterizes the system's ability to accurately deliver therapy to specific regions of interest.…”

Robust automatic rigid registration of MRI and X‐ray using external fiducial markers for XFM‐guided interventional procedures

“…Finally, the rigid transformation between the two sets of beads is achieved by a version of the well-known iterative closest point ͑ICP͒ algorithm 20 and is described in Sec. II D. While previous publications 9,12,13,21 have presented the XFM system as applied to endomyocardial injections, 9 mitral cerclage annuloplasty, 21 and the closure of ventricular septal defects 13 ͑VSDs͒ in a swine model, none have presented the computational method that achieves the automatic registration. In early works, 9,21 the procedure was minimally automated and required extensive, time-consuming, interaction by a skilled human operator to localize the MR and X-ray markers by manual examination of the data.…”

Technology preview: X‐ray fused with magnetic resonance during invasive cardiovascular procedures

“…We observed that external fiducial markers affixed to the skin of patients in this study performed less well than those affixed to the skin of juvenile animals during development [12]. The additional error presumably reflects gravitational shifts of the fiducial markers on loose abdominal skin of older and more obese human subjects, combined with variable respiratory motion.…”

“…In vitro phantom tests showed that the XFM representations of blood vessels were within 1 mm of the true position under X-ray [11]. In animal tests of catheterbased myocardial injection, we reported a target registration error of 3.2 ± 2.6 mm [12].…”

“…Real-time MRI has successfully guided interventional cardiovascular procedures in animal models, but requires specially designed catheter devices not yet available for human use. We have developed an intermediate approach to guide conventional fluoroscopic cardiovascular procedures by fusing 3D roadmaps derived from MRI onto the live 2D X-ray fluoroscopy images [11,12]. Our system provides some of the advanced functionality of interventional MRI using any conventional X-ray fluoroscopy system.…”